The present invention relates to interrupter switch and transformer combinations used in power distribution systems and, more particularly, to the combination of a magnetically actuated vacuum interrupter switch and an oil-filled distribution transformer, the switch being for controlling power to the transformer or the loop connection through the transformer.
When interrupting current to an inductive load, an arc can form between the separating switch contacts. For many years, the practice in the electrical power distribution industry has been the use of loadbreak switching in which contact arcing generated during current interruption physically occurs in an insulating fluid contained within an enclosure. However, the fluids historically in use, such as mineral and silicone oils, are limited in their arc-quenching capabilities. The existence and process of extinguishing the arc causes a breakdown of the insulating medium. In general, when arcing occurs physically within the insulating oil, contamination of the oils results from the formation of by-products. Moreover, gas is generated which acts to raise the system pressure. Venting the enclosure containing insulating oil may be required. Such venting adds to the complexity of the enclosure design. However, liquids are advantageous because of their low cost, ready availability and ease of handling and storage.
Unlike oil, there are no by-products resulting from arc in vacuum or an enclosure containing SF6 gas. Any by-products, formed as a result of arcing in SF6 gas, tend to recombine into the gas after a short period of cooling. No harmful residues are left in the system. No insulation is lost and no venting is required.
Consequently, a need exists for an interrupter that has the insulating characteristics of oil and which does not suffer from disadvantages resulting from the formation of by-products.
The foregoing disadvantages of fluid degradation during switching are overcome by apparatus for interrupting the flow of current in a power distribution system for use with an enclosure containing insulating fluid. The apparatus includes a housing formed from insulating material and having a mounting flange formed along the exterior of the housing. The flange is located so that the housing extends away from the mounting side and the upper side of the flange. An electrical current interrupter, having electrical input and output ends, is positioned in the housing so that a portion lies within the portion of the housing extending away from the flange mounting side. An actuator is mechanically connected to the interrupter to provide the mechanical actuation required to interrupt the current flow between the input and output ends of the interrupter. When the flange is attached to the enclosure, the portion of the housing extending away from the flange mounting side extends into the fluid within the enclosure.
Preferably, the interrupter is either a vacuum interrupter or an interrupter filled with an insulating fluid such as SF6 gas. It is also preferred for the actuator to be a magnetic actuator.
In one embodiment the housing comprises an arm member and a base member, preferably integrally formed. A conductor is connected to the electrical output of the interrupter. It is especially preferred for the base member to be molded around a portion of the conductor. It is also preferred for a current sensor, such as a current transformer, to be positioned proximate the conductor for sensing the current flowing there through.
It is also preferred for a flexible conductor to be electrically connected between the output end of the interrupter and the conductor. In such an embodiment, an insulating rod is mechanically interconnected between the actuator and the output end of the interrupter.